When controlling a motor of an electric compressor or the like, the motor is controlled by detecting a rotation position or a rotation speed of a rotor of the motor using a sensor such as a position sensor or a speed sensor. In this case, since a decrease in reliability accompanied with a high temperature environment, disconnection or the like, an increase in the size of the device (dimensions of the outer frame of the motor, especially axial length), an increase in cost and the like are caused, sensorless control is applied these days. Since the sensorless control is influenced by speed estimation characteristics, it is difficult to suppress oscillation. Therefore, as a measure for that, the technology disclosed in Patent Document 1 is known.
In order to control a motor of a compressor in a sensorless manner, the conventional control device for an electric compressor disclosed in Patent Document 1 has a first command current setting portion which sets a first command current for reducing a rotation speed deviation between a target rotation speed and an actual rotation speed, a second current setting portion which sets a second command current of the motor based on the load fluctuation frequency set from mechanical fluctuation factors of the compressor, a third command current calculation portion which sets a third command current of the motor from the first command current and the second command current, and an inverter switching pattern generation portion which generates a command for motor driving from at least the third command current and the actual rotation speed (estimated from the motor inverter).
In the second command current setting portion, the rotation speed deviation is input to a peak filter using a load fluctuation frequency as a peak frequency to set, as the second command current, the output of the peak filter obtained using a transfer function expressed by the following expression.
That is, the transfer function of the peak filter is expressed as follows:Peak Filter(s)=kω/(s2+ω2)
Here, ω indicates a peak frequency (rad/s) and is determined as a load fluctuation frequency. s indicates the Laplacian operator and k indicates a gain.